JP6887800B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copier or a printer using an electrophotographic method.

In an image forming apparatus using an electrophotographic method, a toner image supported by an image carrier is obtained by applying a transfer voltage to a transfer member arranged opposite to the image carrier such as a drum-shaped photoconductor or an intermediate transfer body. Is electrostatically transferred to a transfer material such as paper or transparency. After that, the transfer material to which the toner image is transferred is conveyed to the fixing means in the transfer nip portion formed by the image carrier and the transfer member, and the toner image is fixed to the transfer material by heating and pressurizing in the fixing means. Will be done. The fixing means includes a heating member such as a heater and a pressurizing member that press-contacts the heating member to form a fixing nip portion, and the heating member receives toner by applying an AC voltage from an AC power source. The image is heated to a temperature at which it can be transferred to the transfer material.

In such an image forming apparatus, when a transfer material that absorbs moisture and has a reduced electrical resistance by being left for a long time in a high temperature and high humidity environment or the like is used, the following image defects may occur. When the transfer material is sandwiched between the fixing nip portions while the toner image is being transferred, the AC voltage is superimposed on the transfer voltage at the transfer nip portion via the transfer material, and the AC voltage is transferred to the transfer voltage at the transfer nip portion. Will fluctuate. As a result, the current flowing from the transfer member toward the image carrier fluctuates due to the waveform component of the AC voltage, causing uneven transferability, and as a result, image defects with uneven shading in the sub-scanning direction of the image (hereinafter referred to as AC banding). ) May appear.

Patent Document 1 is provided with a detection member that detects a current flowing through the transfer member, and AC banding is performed when the fluctuation of the current detected by the detection member while transferring the toner image to the transfer material is larger than a predetermined value. The configuration is disclosed in which the transfer voltage is controlled by determining that the above has occurred.

JP 2011-215538

However, in the configuration of Patent Document 1, the transfer voltage is changed even when the current flowing through the transfer member exceeds a predetermined value due to a factor other than the waveform component of the AC voltage (hereinafter referred to as the AC waveform component). There is a risk. As a result, when it is not necessary to change the transfer voltage, the transfer voltage may be changed, which may cause image defects.

Therefore, the present invention provides an image forming apparatus capable of appropriately setting the voltage applied to the transfer member from the transfer power source when it is detected that the AC voltage is superimposed on the transfer voltage via the transfer material. The purpose is to do.

The present invention comprises an image carrier that carries a toner image, a transfer member that contacts the image carrier to form a transfer portion, and the transfer portion transfers a toner image from the image carrier to a transfer material. A transfer power source that applies a voltage to the transfer member, a first detecting means that is arranged between the transfer member and the transfer power source and for detecting a current flowing through the transfer member, and the transfer power source are controlled. It includes a control means and a fixing means having a heating member arranged on the downstream side of the transfer portion with respect to the transport direction of the transfer material and a pressurizing member that abuts on the heating member to form a fixing portion. The image forming apparatus includes a second detecting means for detecting the temperature or humidity of the ambient environment of the image forming apparatus, and the heating member is arranged so as to face the transfer material sandwiched between the fixing portions. The heating unit heats the transfer material sandwiched between the fixing portions by applying a voltage from the AC power source, and the control means receives a toner image from the image carrier to the transfer material in the transfer unit. The transfer power supply is used according to the result of comparing the frequency obtained from the first detection result input from the first detection means and the predetermined frequency range including the power supply frequency of the AC power supply. When the frequency that can be controlled and is obtained from the first detection result is included in the predetermined frequency range, the control means is input from the second detection means. It is characterized in that the voltage applied from the transfer power source to the transfer member is set according to the detection result.

According to the present invention, there is provided an image forming apparatus capable of appropriately setting a voltage applied from a transfer power source to a transfer member when it is detected that an AC voltage is superimposed on the transfer voltage via a transfer material. It is possible to do.

It is schematic cross-sectional view explaining the image forming apparatus of Example 1. FIG. It is a block diagram of Example 1. It is schematic cross-sectional view explaining the structure of the fixing means of Example 1. FIG. It is a schematic diagram explaining the heating part of Example 1. FIG. It is a schematic diagram explaining the mechanism which the AC voltage superimposes on the transfer voltage in Example 1. FIG. It is a schematic graph explaining the detection of the AC waveform component in Example 1. It is a schematic graph explaining the occurrence of AC banding in Example 1. FIG. It is a schematic diagram explaining the image when AC banding occurs in Example 1. FIG. FIG. 5 is a schematic graph illustrating the control performed when the AC waveform component is detected by the detection means in the first embodiment. It is a flowchart at the time of detecting an AC waveform component in Example 1. FIG. 5 is a schematic diagram illustrating a problem that may occur due to the inability to set an appropriate transfer voltage in the first embodiment. It is a flowchart at the time of setting an appropriate transfer voltage in Example 1. It is a timing chart in Example 2. It is a timing chart in Example 3. It is schematic cross-sectional view explaining the image forming apparatus in other examples.

Hereinafter, preferred embodiments of the present invention will be described in detail, exemplary, with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the following examples should be appropriately changed depending on the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, the scope of the present invention is not intended to be limited unless otherwise specified.

(Example 1)
[Configuration of image forming apparatus]
FIG. 1 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus 100 of the present embodiment, and FIG. 2 is a block diagram of a control system of the image forming apparatus 100 of the present embodiment. As shown in FIG. 2, the image forming apparatus 100 is connected to a personal computer 21 which is a host device. The operation start command and the image signal by the personal computer 21 are transmitted to the controller circuit 23 as a control means built in the image forming apparatus 100. Then, the controller circuit 23 controls various means to execute image formation in the image forming apparatus 100. The controller circuit 23 can control various means based on the detection results input from the various control means and the information input to the image forming apparatus 100 by the user.

As shown in FIG. 1, the image forming apparatus 100 of this embodiment has a photosensitive drum 1 (image carrier) which is a drum-shaped photosensitive member, and the photosensitive drum 1 receives a driving force from a driving source M. It is rotationally driven at a predetermined peripheral speed in the direction of arrow R1 shown in the figure. The photosensitive drum 1 in this embodiment has an outer diameter of 24 mm and is rotationally driven at a peripheral speed of 118 mm / sec.

Around the photosensitive drum 1, a charging roller 2, a charging power source 3 for applying a voltage to the charging roller 2, an exposure means 4, a developing means 5 having a developing roller 5a as a developing member, and a cleaning blade 6a are provided. The cleaning means 6 and the like are arranged. Toner is contained in the developing means 5, and the developing roller 5a supports the toner contained in the developing means 5 by applying a voltage having a polarity opposite to the normal charging polarity of the toner from a developing power source (not shown). It is possible to do.

Further, at a position facing the photosensitive drum 1, a transfer roller 8 as a transfer member that abuts on the photosensitive drum 1 to form a transfer nip portion Nt is arranged. The transfer roller 8 has a core metal and an elastic member such as rubber having conductivity formed on the surface of the core metal. In this embodiment, the outer diameter of the core metal is 5 mm and the thickness of the elastic member. Was 3.75 mm, and the value of the electric resistance of the transfer roller 8 was adjusted in the range of ^{10 7} to 10 ^{9 Ω.} Further, the transfer roller 8 is connected to the transfer power source 18, and a detecting means 19 (first detecting means) for detecting the current flowing toward the transfer roller 8 is provided between the transfer roller 8 and the transfer power source 18. It is provided.

With respect to the transport direction of the transfer material P, a fixing means 14 having a pressurizing member 30 and a heating member 31 is provided on the downstream side of the transfer nip portion Nt. Further, the image forming apparatus 100 is a loading unit for loading a paper feed cassette 9 as an accommodating portion for accommodating a transfer material P such as paper or an OHP sheet, and a transfer material P on which an image is formed and discharged from the image forming apparatus 100. The output tray 17 and the like are provided.

Further, as shown in FIG. 1, the image forming apparatus 100 includes a top sensor 10, an environment sensor 24 (second detection means), a voltage detection means (third detection means), and a media sensor 26 (fourth detection means). Detection means) and. The top sensor 10 can detect the tip of the transfer material P fed from the paper cassette 9 with respect to the transport direction of the transfer material P, and the media sensor 26 can detect the transfer fed from the paper cassette 9. It is possible to determine the type of material P. Further, the environment sensor 24 can detect the temperature and humidity of the ambient environment of the image forming apparatus 100, and the voltage detecting means 25 can detect the voltage of the commercial power source connected to the image forming apparatus 100. It is possible. As shown in FIG. 2, the detection results detected by these various detection means are input to the controller circuit 23.

When the controller circuit 23 (shown in FIG. 2) receives the image signal, the image forming operation is started, and the photosensitive drum 1 is rotationally driven. During the rotation process, the photosensitive drum 1 is uniformly charged to a predetermined potential by a charging roller 2 to which a voltage having a predetermined polarity (negative electrode property in this embodiment) is applied from the charging power source 3. After that, by receiving the exposure according to the image signal by the exposure means 4, an electrostatic latent image corresponding to the target image is formed on the surface of the photosensitive drum 1. The electrostatic latent image is developed by a developing roller 5a carrying toner at the developing position, and is visualized as a toner image on the photosensitive drum 1. In this embodiment, the normal charging polarity of the toner contained in the developing means 5 is negative, and the electrostatic latent image is inverted and developed by the toner charged to the same polarity as the charging polarity of the photosensitive drum 1 by the charging roller 2. ing. However, the present invention is not limited to this, and the present invention can be applied to an image forming apparatus that positively develops an electrostatic latent image with toner charged in a polarity opposite to the charging polarity of the photosensitive drum 1.

The toner image formed on the photosensitive drum 1 is formed in the transfer nip portion Nt by applying a voltage having a polarity opposite to the normal charging polarity of the toner (positive electrode property in this embodiment) from the transfer power source 18 to the transfer roller 8. The transfer material P is transferred from the paper feed cassette 9. The transfer material P transported to the transfer nip portion Nt is sandwiched between the transfer nip portions Nt after the tip is detected by the top sensor 10 provided on the upstream side of the transfer nip portion Nt in the transport direction of the transfer material P. , The toner image is transferred from the photosensitive drum 1. The transfer roller 8 is urged toward the photosensitive drum 1 by an urging means (not shown), and when the toner image is transferred from the photosensitive drum 1 to the transfer material P, the transfer roller 8 rotates the photosensitive drum 1. It follows and rotates.

The value of the electric resistance of the transfer roller 8 varies depending on the temperature and humidity of the ambient environment, the durability of the transfer roller 8, and the like. Therefore, when transferring the toner image from the photosensitive drum 1 to the transfer material P, it is necessary to determine the voltage applied from the transfer power source 18 to the transfer roller 8 according to the fluctuation of the electric resistance value of the transfer roller 8. .. The voltage (hereinafter referred to as transfer voltage Vt) applied from the transfer power source 18 to the transfer roller 8 when the toner image is transferred from the photosensitive drum 1 to the transfer material P is controlled by a control called ATVC (Active Transfer Voltage Control). It is determined. Hereinafter, ATVC will be described.

First, constant current control is performed so that a current of a predetermined value flows through the transfer roller 8 before the transfer material P reaches the transfer nip portion Nt, and the voltage V0 applied from the transfer power supply 18 to the transfer roller 8 at that time is The value of the electric resistance of the transfer roller 8 is estimated from the value. The current flowing through the transfer roller 8 is detected by the detection means 19, and the controller circuit 23 controls the transfer power supply 18 according to the detection result input from the detection means 19, so that constant current control is performed. Then, according to the estimated value of the electric resistance of the transfer roller 8 and the value of the voltage V0, the controller circuit 23 refers to the look-up table (LUT) recorded in advance in the built-in memory, and transfers the transfer voltage Vt (No. 1). 1 voltage) is determined. After that, the controller circuit 23 feeds back the determined transfer voltage Vt to the transfer power supply 18, and applies the transfer voltage Vt from the transfer power supply 18 to the transfer roller 8, whereby the toner image is transferred to the transfer material P at the transfer nip portion Nt. Will be done.

In this embodiment, when the toner image is transferred from the photosensitive drum 1 to the transfer material P, the controller circuit 23 transfers the transfer power supply 18 so that a constant current flows from the transfer roller 8 toward the photosensitive drum 1. To control. At this time, the controller circuit 23 controls the transfer power supply 18 according to the value of the current detected by the detecting means 19, and performs constant current control. However, when such constant current control is performed, the following problems may occur when the toner image is transferred to the transfer material P having a low electric resistance at the transfer nip portion Nt.

When constant current control is performed when the toner image is transferred from the photosensitive drum 1 to the transfer material P whose electrical resistance has decreased due to moisture absorption or the like, the controller circuit 23 transfers from the transfer power supply 18 due to the low electrical resistance of the transfer material P. Control is performed to reduce the voltage applied to the roller 8. However, the current flowing from the transfer roller 8 to the photosensitive drum 1 leaks to each member in contact with the transfer material P via the transfer material P whose electrical resistance has decreased. Therefore, at this time, the photosensitive drum at the transfer nip portion Nt. There is a risk that the current for transferring the toner image from 1 to the transfer material P will be insufficient. As a result, transfer defects may occur.

Therefore, in this embodiment, the lower limit voltage Vtl is set with respect to the transfer voltage Vt applied from the transfer power supply 18 to the transfer roller 8. By setting the lower limit voltage Vtl, it is possible to suppress the shortage of the current flowing from the transfer roller 8 to the photosensitive drum 1 in the transfer nip portion Nt. That is, in this embodiment, the controller circuit 23 performs constant current control when the transfer voltage Vt is larger than the lower limit voltage Vtl, and by constant voltage control when the transfer voltage Vt reaches the lower limit voltage Vtl. The transfer power supply 18 is controlled. When performing constant voltage control, a lower limit voltage Vtl is applied from the transfer power supply 18 to the transfer roller 8. In this embodiment, the lower limit voltage Vtl is set by the calculation formula from the voltage V0 obtained when performing ATVC, but the present invention is not limited to this, and the look-up table (LUT) is set according to the value of the voltage V0 like the transfer voltage Vt. ) May be set as the lower limit voltage Vtl.

The transfer material P to which the toner image is transferred by the transfer nip portion Nt is transferred to the fixing means 14 after the charge accumulated on the surface of the transfer material P is removed by the static elimination member 20. Then, the toner image is fixed to the transfer material P by being heated and pressurized by the heating member 31 and the pressurizing member 30 in the fixing means 14. The toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the toner image is transferred to the transfer material P is cleaned and removed by the cleaning blade 6a and collected by the cleaning means 6. The transfer material P after the toner image is fixed by the fixing means 14 is discharged to the paper discharge tray 17 by the paper discharge roller pair 16. In the image forming apparatus of this embodiment, an image is formed on the transfer material P by the above operation.

[Fixing means]
In this embodiment, a film fixing method was used as the fixing means. FIG. 3 is a schematic cross-sectional view illustrating the configuration of the fixing means 14 in this embodiment. As shown in FIG. 3, the fixing means 14 includes a pressurizing member 30 and a heating member 31, and the pressurizing member 30 presses the heating member 31 to transfer the toner image to the transfer material P. A fixing nip portion Nf is formed as a fixing portion capable of sandwiching the above.

The pressurizing member 30 has an outer diameter of 14 mm and has a core metal 30a, an elastic layer 30b formed on the outer peripheral surface side of the core metal 30a, and a mold release layer 30c formed on the outer peripheral surface side of the elastic layer 30b. Laura. As the elastic layer 30b, silicone rubber, fluororubber, or the like can be used, and as the release layer 30c, a fluororesin such as a tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) can be used. The pressurizing member 30 is rotatably supported at both ends of the core metal 30a in the longitudinal direction.

The heating member 31 includes a film 31a, a plate-shaped heater 31b at a position facing the pressure member 30 via the film 31a and in contact with the inner peripheral surface of the film 31a, and a support portion 31c for supporting the heater 31b. , A pressure stay 31d that reinforces the support portion 31c. The heater 31b as a heating portion is arranged in the fixing nip portion Nf, and an AC voltage is applied from the commercial power supply 52 (AC power supply) via the bidirectional thyristor 51 (TRIAC). The controller circuit 23 can switch ON / OFF of the bidirectional thyristor 51 by controlling the current flowing through the gate of the bidirectional thyristor 51, and the AC voltage applied to the heater 31b is controlled to raise the temperature of the heater 31b. It will be adjusted.

The film 31a is a cylinder having a base layer (not shown), an elastic layer formed on the outer peripheral surface side of the base layer (not shown), and a release layer (not shown) formed on the outer peripheral surface side of the elastic layer. It is a flexible member in the shape of a shape. The base layer of the film 31a needs to have heat resistance for receiving the heat of the heater 31b and durability for rubbing against the heater 31b, and a metal such as stainless steel or nickel or a heat resistant resin such as polyimide is used. Is preferable. Further, it is preferable to use a fluororesin such as a perfluoroalkoxy resin (PFA) or a polytetrafluoroethylene resin (PTFE) for the release layer of the film 31a. The film 31a in this example had an outer diameter of 18 mm, used a polyimide having a thickness of about 60 μm as a base layer, and used a silicone rubber having a thickness of about 150 μm as an elastic layer. As the release layer, PFA having excellent mold release property and heat resistance was used among the fluororesins, and the thickness of the release layer was set to 10 μm.

FIG. 4A is a schematic view illustrating the configuration of the heater 31b when viewed from the direction of arrow A in FIG. 3, and FIG. 4B is a schematic diagram when viewed from the direction of arrow B in FIG. 4A. It is a schematic diagram explaining the structure of the heater 31b at the time. As shown in FIG. 4A, the heater 31b is a heat-generating resistor made of a silver-palladium alloy by screen printing on an alumina substrate b1 having a width of 6 mm in the transport direction of the transfer material P and a thickness of 1 mm in the thickness direction. b2 is formed with a thickness of about 10 μm. An electrode portion b3 is provided on one end side of the heat generation resistor b2, and the electrode portion b3 is electrically connected to the commercial power supply 52. Due to the AC voltage applied from the commercial power source 52 to the electrode portion b3, a current flows through the electrode portion b3 to the heat generation resistor b2, and the heat generation resistor b2 generates heat. Further, as shown in FIG. 4B, the heater 31b has a protective layer b4 that protects the heat generating resistor b2, and the protective layer b4 has a thickness of 60 μm and is formed by a glass coat.

As shown in FIG. 3, a thermistor 31e for detecting the temperature of the heater 31b is attached to the surface of the heater 31b opposite to the surface in contact with the film 31a. The controller circuit 23 controls ON / OFF of the bidirectional thyristor 51 according to the detection result by the thermistor 31e, and this control adjusts the amount of the current flowing through the heat generating resistor b2 and adjusts the temperature of the heater 31b.

The support portion 31c is formed of a liquid crystal polymer and has rigidity, heat resistance, and heat insulating properties. The support portion 31c has a role of supporting the inner peripheral surface of the film 31a in contact with the support portion 31c and a role of supporting the heater 31b. The pressure stay 31d has a U-shaped cross section when viewed from the longitudinal direction in order to increase the bending rigidity of the heating member 31, and is formed by bending stainless steel having a plate thickness of 1.6 mm. Has been done.

When the toner image is fixed to the transfer material P by the fixing means 14, the rotational force from the drive source M is transmitted to the pressurizing member 30, and as shown in FIG. 3, the pressurizing member 30 is designated in the direction of arrow R2 in the drawing. It is driven to rotate at speed. As a result, the film 31a rotates in accordance with the rotation of the pressurizing member 30 while sliding with the heater 31b.

The transfer material P is introduced into the fixing nip portion Nf in a state where the film 31a and the pressurizing member 30 rotate, the heater 31b is energized, and the temperature detected by the thermistor 31e of the heater 31b reaches the target temperature. The toner image transferred to the transfer material P by the transfer nip portion Nt is heated and pressurized in the process of the transfer material P passing through the fixing nip portion Nf, and is melt-fixed to the transfer material P. The transfer material P that has passed through the fixing nip portion Nf is separated from the film 31a by the curvature of the film 31a, and is discharged to the paper ejection tray 17 by the paper ejection roller pair 16.

The distance from the transfer nip portion Nt of the image forming apparatus 100 to the fixing nip portion Nf in this embodiment is 40 mm. Therefore, when an image is formed on a normal A4 size or letter size transfer material P, the toner image is fixed on the transfer material P by the fixing means 14, and at the same time, the transfer material is transferred from the photosensitive drum 1 at the transfer nip portion Nt. The toner image is transferred to P.

[Mechanism of AC banding]
Next, when an image is formed on a transfer material P having a low electrical resistance such as a transfer material P that has absorbed moisture, the AC voltage of the commercial power supply 52 is superimposed on the transfer voltage Vt in the transfer nip portion Nt via the transfer material P. The image defect that occurs in FIG. 5 will be described with reference to FIGS. 5 to 8. FIG. 5 is a schematic diagram illustrating a mechanism in which image defects occur when the AC voltage of the commercial power supply 52 is superimposed on the transfer voltage Vt in the transfer nip portion Nt. The transfer material P in the following description is a transfer material P that has been left for a long time in a high temperature and high humidity environment to absorb moisture, and the length of the transfer material P in the transport direction is from the transfer nip portion Nt to the fixing nip portion Nf. It is A4 size paper longer than 40 mm, which is the distance of.

When the transfer material P is sandwiched between the fixing nip portions Nf in a state where the toner image is transferred from the photosensitive drum 1 by the transfer nip portion Nt of the transfer material P that has absorbed moisture by being left in a high temperature and high humidity environment or the like. An AC voltage is applied from the commercial power supply 52 to the heater 31b. FIG. 5 The transfer material P sandwiched between the fixing nip portions Nf is in contact with the film 31a in the heating member 31, and the film 31a is in contact with the heater 31b in the fixing nip portion Nf. As shown in FIG. 4A, the heater 31b has a conductive alumina substrate b1 having low electrical resistance and an electrode portion b3 formed on the substrate b1, and the commercial power supply 52 has an electrode portion. An AC voltage is applied to b3.

As shown in FIG. 5, when the electric resistance of the transfer material P is low, the AC voltage applied to the heater 31b fluctuates the transfer voltage Vt in the transfer nip portion Nt via the film 31a and the transfer material P. As a result, the current flowing from the transfer roller 8 toward the photosensitive drum 1 is swayed by the waveform component of the AC voltage of the commercial power supply 52 (hereinafter referred to as the AC waveform component).

FIG. 6A is a schematic graph illustrating the current detected by the detection means 19 when the AC voltage of the commercial power supply 52 is superimposed on the transfer voltage Vt in the transfer nip portion Nt. FIG. 6B is a schematic graph in which the waveform of the current swayed by the AC waveform component in FIG. 6A is enlarged.

The time T1 in FIG. 6A is the time when the transfer material P rushes into the transfer nip portion Nt, and the time T2 is the time when the transfer material P rushes into the fixing nip portion Nf. In the state before the time T2, the transfer material P is not sandwiched by both the transfer nip portion Nt and the fixing nip portion Nf, so that the AC voltage of the commercial power supply 52 is transferred via the transfer material P. Does not superimpose on. On the other hand, after the time T2 when the transfer material P is sandwiched by both the transfer nip portion Nt and the fixing nip portion Nf, the AC voltage of the commercial power supply 52 is superimposed on the transfer power supply via the transfer material P, and the AC waveform component. The current fluctuates. As a result, as shown in FIG. 6B, the current flowing through the transfer roller 8 fluctuates in the power frequency cycle of the commercial power supply 52. The time T3 is the time when the transfer material P has passed the fixing nip portion Nt, and at this time, the transfer material P is not sandwiched by both the transfer nip portion Nt and the fixing nip portion Nf.

FIG. 7A shows that the appropriate range of the value of the current flowing from the transfer roller 8 to the photosensitive drum 1 in order to transfer the toner image from the photosensitive drum 1 to the transfer material P differs depending on the value of the electrical resistance of the transfer material P. It is a schematic diagram explaining. Further, FIG. 7B is a schematic graph illustrating an image defect (hereinafter referred to as AC banding) caused by the current flowing from the transfer roller 8 toward the photosensitive drum 1 being shaken by the AC waveform component. Is. FIG. 8 is a schematic view of an image of AC banding.

As shown in FIG. 7A, the toner image is transferred to the transfer material P which has absorbed moisture and the electric resistance is low, and the toner image is transferred to the transfer material P which is not absorbing moisture and has low electric resistance. The appropriate range of the value of the current flowing through the photosensitive drum 1 is different from that of the case where Hereinafter, the transfer material P having absorbed moisture and having a low electric resistance will be referred to as a hygroscopic paper, and the transfer material P which has not absorbed moisture and has a low electric resistance immediately after being released from the wrapping paper will be referred to as a straight paper. I do.

Since the hygroscopic paper absorbs moisture more than the straight paper, the electric resistance is low, and the current flowing from the transfer roller 8 to the photosensitive drum 1 tends to leak through the hygroscopic paper. Therefore, it is necessary to pass a large amount of current from the transfer roller 8 to the photosensitive drum 1, and it is necessary to apply a high transfer voltage Vt from the transfer power source 18 to the transfer roller 8. On the other hand, when a high transfer voltage Vt is applied to the open paper, an excessive current flows from the transfer roller 8 to the photosensitive drum 1 through the open paper, so that the polarity of the toner in the transfer nip portion Nt is reversed. There is a risk that the paper will be transferred from the open paper to the photosensitive drum 1 in reverse. This is because the open straight paper has a lower electrical resistance than the hygroscopic paper, so that the current leaking through the open straight paper is small.

Therefore, as shown in FIG. 7A, the current flowing from the transfer roller 8 to the photosensitive drum 1 includes an appropriate range of the current when transferring the toner image to the moisture absorbing paper and the toner image is transferred to the open paper. The value of the current in the range where the appropriate ranges of the currents overlap is preferable. In this embodiment, a transfer voltage Vt is applied from the transfer power supply 18 to the transfer roller 8 so that a current in a range in which the appropriate ranges overlap in FIG. 7A flows.

When the transfer voltage Vt set in this way is applied from the transfer power supply 18 to the transfer roller 8, when the AC voltage of the commercial power supply 52 is superimposed on the transfer voltage Vt, the current flowing from the transfer roller 8 to the photosensitive drum 1 is AC. It fluctuates depending on the waveform component, and the waveform is as shown in FIG. 7 (b). At this time, the current flowing from the transfer roller 8 to the photosensitive drum 1 fluctuates in the power frequency cycle of the commercial power supply 52, so that the valley portion of the waveform in FIG. 7B is the current when the toner image is transferred to the moisture absorbing paper. It falls below the proper range. As a result, the current is insufficient in the power frequency cycle of the commercial power supply 52, and as shown in FIG. 8, the image transferred from the photosensitive drum 1 to the transfer material P after the transfer material P rushes into the fixing nip portion Nf is displayed. This is an image of AC banding in which density unevenness occurs in the power frequency cycle of the commercial power supply 52.

[Detection of AC waveform components]
In this embodiment, when the controller circuit 23 detects an AC waveform component according to the detection result input from the detection means 19, the controller circuit 23 controls the transfer power supply 18 to change the transfer voltage Vt. Below, in a high temperature and high humidity environment with a room temperature of 32.5 degrees and a humidity of 80%, the transfer material P (basis weight 80 g / m ² ) of Oce A4 size paper RedLabel left in the same high temperature and high humidity environment for 48 hours or more is entirely black. The control of this embodiment when the solid image of the above is formed will be described in detail.

The peripheral speed of the photosensitive drum 1 in this embodiment is 118 mm / sec, the voltage of the commercial power supply 52 is 220 V, and the power supply frequency is 50 Hz. Further, the value of the voltage V0 when the ATVC control was performed so that a current of 3 μA flowed was 500 V. From this result, the controller circuit 23 set the transfer voltage Vt applied from the transfer power source 18 to the transfer roller 8 when transferring the toner image from the photosensitive drum 1 to the transfer material P to 750 V, and started image formation.

FIG. 9A is a graph illustrating a current detection result measured by the detection means 19 when the AC voltage from the commercial power supply 52 is superimposed on the transfer voltage Vt. 9 (b) is a graph when the simple moving average of the detection result of FIG. 9 (a) is taken, and FIG. 9 (c) is the detection result of taking the simple moving average twice in FIG. 9 (b). It is an enlarged graph of the waveform of. Further, FIG. 10 is a flowchart illustrating control when detecting an AC waveform component.

The current flowing through the transfer roller 8 is detected by the detecting means 19, and the detection result is input to the controller circuit 23. As shown in FIG. 10, when the image formation is started and the tip of the transfer material P reaches the fixing nip portion Nf, the signal input from the detection means 19 to the controller circuit 23 is updated at 1 ms intervals. At this time, the detection means 19 detects a signal containing noise as shown in FIG. 9A. Therefore, in this embodiment, in order to remove this noise, a simple moving average of the detection results (first detection results) obtained in FIG. 9 (a) is taken, and the waveform C (b) in FIG. 9 (b) is taken. The first waveform) and the waveform D (second waveform) were obtained.

The simple moving average can be considered as a low-pass filter, and a suitable gain G for taking the simple moving average in order to obtain a waveform in which the amplitude of a frequency higher than the signal frequency f is attenuated can be expressed by the following equation 1. The power frequency of the commercial power supply 52 in this embodiment is 50 Hz, and in the detection result of FIG. 9A, in order to remove the amplitude of the frequency higher than 60 Hz as noise, the waveform C and the waveform D are obtained by using Equation 1. Obtained. In the waveform of the detection result of FIG. 9A acquired at 1 ms intervals, the number of points at which the amplitude of frequencies higher than 60 Hz is attenuated (gain becomes 1 / √2) was obtained from Equation 1 and found to be a simple moving average. The score to be taken (moving average score) was 7 points.

（Ｇ：ゲイン、τ＝Ｍ（移動平均点数）×Δｔ（サンプリング間隔＝１ｍｓ）、ｆ：信号周波数＝６０Ｈｚ）

(G: gain, τ = M (moving average score) × Δt (sampling interval = 1 ms), f: signal frequency = 60 Hz)

The waveform C shown in FIG. 9B is a waveform obtained when a simple moving average is taken with a moving average score of 7 points with respect to the waveform of the detection result of FIG. 9A. If noise remains in the waveform even if the simple moving average is taken once, as in waveform C, it is better to take the simple moving average of waveform C again than to increase the number of moving average points and take the simple moving average. The phase shift and the decrease in amplitude can be suppressed to a small extent. Therefore, in order to make it easier to detect the power frequency of the commercial power supply 52, in this embodiment, a simple moving average is taken with respect to the waveform C with a moving average score of 7 points to obtain a waveform D.

With respect to the waveform D thus obtained, as shown in FIG. 9C, it is determined that the point where the slope of the waveform changes (inflection point) is the peak, and the time interval ΔT between adjacent peaks The frequency obtained from the above is compared with a predetermined frequency range including the power supply frequency of the commercial power supply 52. In FIG. 9C, the peak E in which the slope of the waveform D changes from positive to negative is defined as the first peak, and the peak F in which the slope of the waveform D changes from negative to positive is defined as the second peak. As shown in FIGS. 9 (c) and 10 in this embodiment, the frequency 1 / 2ΔT was obtained from the time interval ΔT between the peak E and the peak F (between half cycles).

Further, in this embodiment, the difference (difference ΔI) in the current values between the adjacent peaks E and F is obtained, and the frequency 1 when the value of the difference ΔI is equal to or more than a predetermined value. The / 2ΔT and the difference ΔI were stored. The value of the difference ΔI can be set according to the control of the image forming apparatus 100, and in this embodiment, the predetermined value of the difference ΔI is set to 1 μA. After that, as shown in FIG. 10, in the controller circuit 23, the value of the frequency 1 / 2ΔT is included in the predetermined frequency range including the power supply frequency of the commercial power supply 52, and the difference ΔI is equal to or more than the predetermined value. Determine if there is.

Here, since the power frequency of the commercial power supply 52 used this time is 50 Hz, it is said that the AC waveform component is detected when the value of the frequency 1 / 2ΔT is included in the predetermined frequency range of 40 Hz <1 / 2ΔT <60 Hz. It is possible to judge. Then, the controller circuit 23 determines that the AC waveform component has been detected when the value of the frequency 1 / 2ΔT is included in the range of 40 Hz <1 / 2ΔT <60 Hz and the difference ΔI is 1 μA or more, and the previous time. The number of detections added once with respect to the number of detections of is stored. When the value of the frequency 1 / 2ΔT is included in the range of 40Hz <1 / 2ΔT <60Hz and the condition that the difference ΔI is 1 μA or more is not satisfied, the controller circuit 23 detects the AC waveform component. Remember that the number of times is 0.

As shown in FIG. 10, in this embodiment, the controller circuit 23 controls to change the transfer voltage Vt when it is determined that the AC waveform component has been detected more than a predetermined number of times. The current flowing through the transfer roller 8 may fluctuate due to the moment when the transfer material P rushes into the fixing nip portion Nf, a change in the amount of toner carried by the photosensitive drum 1, and the like. Therefore, in order to remove such noise and determine the presence or absence of AC banding with high accuracy, it is preferable to change the transfer voltage Vt when the number of detections of the AC waveform component is a predetermined number or more.

For example, when the predetermined number of times is set to 2, the value of the frequency 1 / 2ΔT is included in the range of 40Hz <1 / 2ΔT <60Hz, and the difference ΔI is different between the three consecutive peaks. When it is 1 μA or more, the transfer voltage Vt is changed. The predetermined number of times is preferably at least 2 times or more, and in this embodiment, the predetermined number of times is set to 4 times, and the difference ΔI and the frequency 1 / 2ΔT between five consecutive peaks (between 2.5 cycles) Was compared. The detection accuracy of the AC waveform component can be further improved by comparing more peaks, but the detection time becomes longer when the predetermined number of times is increased. Therefore, in this embodiment, the predetermined number of times is set to 4 in order to accurately determine the presence or absence of AC banding by the controller circuit 23 and sufficiently obtain the effect of suppressing the occurrence of image defects. ..

When the value of the frequency 1 / 2ΔT is included in the predetermined frequency range of 40Hz <1 / 2ΔT <70Hz, the controller circuit 23 may be set to determine that the AC waveform component has been detected. With such a setting, both a power supply frequency of 50 Hz and a power supply frequency of 60 Hz can be included in a predetermined frequency range, and the AC waveform can be included regardless of whether the power supply frequency of the commercial power supply is 50 Hz or 60 Hz. It is possible to detect the components.

[Control to set the transfer voltage appropriately]
In this embodiment, the controller circuit 23 provides a condition for determining whether or not the transfer voltage Vt is changed in order to set a more appropriate transfer voltage when it is determined that AC banding has occurred. Hereinafter, it will be described with reference to FIGS. 11 and 12. FIG. 11 is a schematic diagram illustrating a problem that may occur due to the inability to set an appropriate transfer voltage when it is determined that AC banding has occurred, and FIG. 12 is a schematic diagram for setting an appropriate transfer voltage in this embodiment. It is a flowchart for doing.

In FIG. 11, the waveform G is a waveform for explaining a case where a transfer voltage Vt is applied from the transfer power supply 18 to the transfer roller 8 and an AC waveform component is detected a predetermined number of times or more, but no image defect occurs. The waveform H is a waveform of a current detected by the detection means 19 when the controller circuit 23 determines that AC banding has occurred and raises the transfer voltage Vt according to the detection result of the waveform G. As shown in FIG. 11, even when the AC waveform component is detected more than a predetermined number of times, it is appropriate for the photosensitive drum 1 from the transfer roller 8 as in the waveform G, depending on the preset transfer voltage Vt value. Current may flow. In such a state, if the controller circuit 23 changes the transfer voltage Vt to a larger value, the peak portion of the waveform H exceeds the appropriate current range as shown in the waveform H, and the photosensitive drum There is a risk that an excessive current will flow through 1.

Therefore, in this embodiment, as shown in FIG. 12, when it is determined that the AC waveform component has been detected more than a predetermined number of times, the current flowing from the transfer roller 8 to the photosensitive drum 1 is insufficient, resulting in image defects. Control is performed to change the transfer voltage Vt to a larger value only when it occurs. That is, when it is considered that the AC waveform component is detected more than a predetermined number of times and the valley portion of the current waveform detected by the detection means 19 falls below the appropriate current range, the transfer voltage Vt is changed to be appropriate. If it is considered that the current does not fall below the current range, the transfer voltage Vt is not changed. The controller circuit 23 determines from the information input to the controller circuit 23 whether the condition for increasing the transfer voltage Vt is satisfied, and changes the transfer voltage Vt to a larger value. Hereinafter, the conditions under which the controller circuit 23 raises the transfer voltage Vt will be described.

<When the electrical resistance of the transfer material P is low>
When the electrical resistance of the transfer material P is low, it is conceivable that the current flowing from the transfer roller 8 to the photosensitive drum 1 leaks through the transfer material P. That is, the current required to transfer the toner image to the transfer material P is the appropriate range of the current when transferring the toner image to the moisture absorbing paper in FIG. 7A, and the toner image is transferred to the open paper. It is conceivable that the value is near the lower limit of the range in which the appropriate range of the current overlaps. Therefore, when the AC waveform component is detected more than a predetermined number of times when the toner image is transferred to the transfer material P having low electrical resistance, the transfer roller 8 is transferred to the photosensitive drum 1 as shown in FIG. 7B already described. There is a risk that AC banding will occur due to a partial shortage of flowing current.

In this embodiment, first, is the toner image transferred to the transfer material P having low electrical resistance in the transfer nip portion Nt by the detection result (second detection result) input from the environment sensor 24 to the controller circuit 23? I decided. When the ambient environment of the image forming apparatus 100 is high temperature or high humidity, it is considered that the electric resistance of the transfer material P housed in the paper feed cassette 9 is low. Therefore, when the temperature or humidity detection result (second detection result) detected by the environment sensor 24 is equal to or higher than a predetermined value, the transfer voltage Vt is changed to a larger value by the controller circuit 23 to obtain AC. The generation of banding images can be suppressed.

The environment sensor 24 can be arranged at a position inside the image forming apparatus 100 that is not easily affected by self-heating. Further, in this embodiment, the surrounding environment is determined from the detection result input from the environment sensor 24 to the controller circuit 23, but the present invention is not limited to this. For example, the image forming apparatus 100 is not provided with the environment sensor 24, and the ambient environment is determined according to the surrounding environment data input from the personal computer 21 to the controller circuit 23 and the surrounding environment data input by the user to the image forming apparatus 100. You may judge.

Further, the electrical resistance of the transfer material P varies not only with the fluctuation due to the surrounding environment but also with the basis weight of the transfer material P and the components contained in the transfer material P. In general, the transfer material P having a large basis weight tends to have a high electrical resistance. Therefore, for example, when the type of the transfer material P is known in advance by the print mode input by the user, the controller circuit 23 determines that the transfer material P has a large basis weight and changes the transfer voltage Vt to a larger value. Therefore, the occurrence of AC banding can be suppressed. Alternatively, the media sensor 26 provided in the image forming apparatus 100 may determine the type of the transfer material P to be conveyed to the transfer nip portion Nt. When the print mode or the information of the transfer material P input to the image forming apparatus 100 by the user is used to determine the type of the transfer material P, the image forming apparatus 100 may or may not be provided with the media sensor 26. You may.

Further, the value of the current detected by the detecting means 19 when the transfer material P is not sandwiched between the transfer nip portions Nt and the current detected by the detecting means 19 when the transfer material P is sandwiched between the transfer nip portions Nt. The electrical resistance of the transfer material P may be estimated by comparing with the value. The current detection result and the transfer power supply 18 detected by the detection means 19 after the tip of the transfer material P is sandwiched between the transfer nip portions Nt and before the tip of the transfer material P reaches the fixing nip portion Nf. The electrical resistance of the transfer material P can be estimated from the voltage applied to the transfer roller 8. When the estimated electrical resistance of the transfer material P is lower than a predetermined value, the controller circuit 23 determines that the transfer material P has a low electrical resistance and changes the transfer voltage Vt to a larger value, thereby AC. The occurrence of banding can be suppressed.

Further, when the transfer voltage Vt applied from the transfer power source 18 to the transfer roller 8 when transferring the toner image to the transfer material P is the lower limit voltage Vtl, the electrical resistance of the transfer material P sandwiched between the transfer nip portions Nt. Is considered to be low. Therefore, when the lower limit voltage Vtl is applied from the transfer power supply 18 to the transfer roller 8 when the AC waveform component is detected, the occurrence of AC banding is suppressed by applying a voltage having a value larger than the lower limit voltage Vtl. Can be done.

<When the output voltage of the commercial power supply 52 is large>
When the AC voltage of the commercial power supply 52 is superimposed on the transfer voltage Vt, the fluctuation width of the current flowing from the transfer roller 8 to the photosensitive drum 1 varies depending on the magnitude of the voltage of the commercial power supply 52. When the value of the voltage output from the commercial power supply 52 is large, the fluctuation width of the current flowing from the transfer roller 8 to the photosensitive drum 1 becomes large, so that the current flowing from the transfer roller 8 to the photosensitive drum 1 is partially insufficient. AC banding may occur. Therefore, when the controller circuit 23 detects the AC waveform component more than a predetermined number of times and the voltage of the commercial power supply 52 detected by the voltage detecting means 25 is larger than the predetermined value, the transfer voltage Vt is set to a larger value. May be changed to.

In this embodiment, the transfer voltage Vt is changed from 750V to 780V when the controller circuit 23 detects the AC waveform component more than a predetermined number of times and determines that the condition for increasing the transfer voltage Vt is satisfied. did. This makes it possible to suppress transfer unevenness due to insufficient current as shown in FIG. 7B.

As described above, in the present embodiment, when the AC waveform component is detected by the controller circuit 23 more than a predetermined number of times, an appropriate transfer voltage can be set according to the information input to the controller circuit 23. Is. It should be noted that it may be determined whether or not the condition for increasing the transfer voltage Vt is satisfied by using only one of the above-mentioned conditions, and it is determined whether or not the condition for increasing the transfer voltage Vt is satisfied by combining a plurality of conditions. You may.

In the transfer nip portion Nt, the electrical resistance between the transfer material P and the photosensitive drum 1 changes depending on the amount of toner transferred from the photosensitive drum 1 to the transfer material P, and the current signal detected by the detection means 19 is transmitted. There is a possibility of swinging. In order not to erroneously detect this current fluctuation as the current fluctuation due to the AC waveform component, information on the printing rate regarding the transport direction of the transfer material P is obtained in advance, and the current fluctuation is predicted and corrected according to the information. May be done. Alternatively, in order to prevent erroneous detection, the detection of the AC waveform component may be temporarily stopped for a predetermined time from the timing when the print rate changes.

Similarly, the signal of the current detected by the detecting means 19 may fluctuate due to the uneven thickness of the photosensitive drum 1 in the circumferential direction, the fluctuation of the electric resistance of the transfer roller 8, and the like. Therefore, for example, before the transfer material P reaches the transfer nip portion Nt or between papers between the transfer materials P, the current flowing from the transfer power source 18 to the transfer roller 8 is detected by the detecting means 19, and the result is an AC waveform. It may be reflected in the detection of the component. That is, the fluctuation of the electrical resistance of the photosensitive drum 1 and the transfer roller 8 is predicted from the value of the current detected by the detection means 19 while the transfer material P is not sandwiched between the transfer nip portions Nt, and the AC waveform component is detected. The conditions or the detection result may be corrected.

Further, in this embodiment, a configuration is used in which the detection means 19 detects the periodic fluctuation of the current flowing through the transfer roller 8, but the present invention is not limited to this. The same effect as that of the present invention can be obtained even in a configuration in which the voltage output from the transfer power supply 18 is detected to detect the periodic fluctuation of the transfer voltage Vt when the toner image is transferred to the transfer material P. Can be done. When detecting the transfer voltage Vt, a detection means such as arranging a detection resistor having a known resistance value between the transfer roller 8 and the transfer power supply 18 is provided between the transfer roller 8 and the transfer power supply 18. The voltage detection circuit may be provided.

(Example 2)
In the first embodiment, the control by the controller circuit 23 when it is determined that AC banding has occurred for one transfer material P has been described. On the other hand, in the second embodiment, the control of the controller circuit 23 in the case where the image is continuously formed on the plurality of transfer materials P (hereinafter referred to as continuous printing) will be described with reference to FIG. In this embodiment, when the continuous print job is executed, the transfer voltage set by the controller circuit 23 with respect to the first transfer material P1 is applied to the second transfer material P2 following the first transfer material P1. It is a configuration that reflects on the transfer voltage of. Therefore, the same configurations and controls as in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

FIG. 13 is a timing chart when the controller circuit 23 controls the transfer power supply 18 in this embodiment. As shown in FIG. 13, when the top sensor 10 detects the tip of the first transfer material P1 with respect to the transfer direction of the transfer material, the controller circuit 23 causes the tip of the first transfer material P to reach the transfer nip portion Nt. A transfer voltage Vt is applied from the transfer power supply 18 to the transfer roller 8 at the timing. After that, when the controller circuit 23 detects the AC waveform component more than a predetermined number of times and determines that the condition for increasing the transfer voltage Vt is satisfied, the transfer voltage Vt is transferred with a larger absolute value. Change to voltage Vt2. At this time, in the transfer nip portion Nt, the toner image is transferred from the photosensitive drum 1 to the first transfer material P1 by the current flowing from the transfer roller 8 to which the transfer voltage Vt2 is applied to the photosensitive drum 1.

In this embodiment, when the toner image is transferred to the first transfer material P1, if the subsequent image forming job to the second transfer material P2 remains, the second transfer material P2 is used. The AC waveform component is not detected. The transfer material P housed in the paper feed cassette 9 is placed in the same environment, and it can be considered that the types and states of the transfer material P are substantially similar. Therefore, with respect to the second transfer material P, the voltage applied from the transfer power supply 18 to the transfer roller 8 by the controller circuit 23 at the timing when the second transfer material P2 is sandwiched between the fixing nip portions Nf is applied to the transfer voltage Vt2. Change to. As a result, it is possible to set an appropriate transfer voltage for the second transfer material P and suppress the occurrence of AC banding.

As described above, in this embodiment, when the continuous printing job is executed, it is determined whether or not AC banding is generated by the controller circuit 23 with respect to the second transfer material P2 following the first transfer material P1. Absent. With this configuration, it is possible to suppress the occurrence of AC banding while reducing the number of detections of AC waveform detection when executing a continuous print job.

(Example 3)
In the second embodiment, the controller circuit 23 applies a voltage applied to the transfer roller 8 from the transfer power supply 18 to the transfer voltage at the timing when the second transfer material P2 following the first transfer material P1 reaches the fixing nip portion Nf. The control to change to Vt2 has been described. On the other hand, in the third embodiment, when the continuous printing job is executed, the transfer voltage Vt2 is applied from the transfer power source 18 to the transfer roller 8 at the timing when the second transfer material P2 reaches the transfer nip portion Nt. It differs from Example 2 in that it is different from Example 2. The configuration of this embodiment is the same as that of the second embodiment except that the transfer voltage Vt2 is applied from the transfer power source 18 to the transfer roller 8 at the timing when the second transfer material P2 reaches the transfer nip portion Nt. Yes, the same points as in the second embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 14 is a timing chart when the controller circuit 23 in this embodiment controls the transfer power supply 18. As shown in FIG. 14, in this embodiment, the transfer voltage Vt2 is applied from the transfer power supply 18 to the transfer roller 8 at the timing when the tip of the second transfer material P2 reaches the transfer nip portion Nt in the transfer direction of the transfer material. It is being applied. The transfer voltage Vt2 is a voltage applied to the transfer roller 8 from the transfer power supply 18 when the controller circuit 23 determines that AC banding has occurred with respect to the first transfer material P1 and changes the transfer voltage Vt. ..

As described in the first embodiment, as a condition in which AC banding is likely to occur, it is conceivable that an image is formed on the transfer material P having a low electrical resistance. When an image is formed on a transfer material P having a low electric resistance, the current flowing from the transfer roller 8 toward the photosensitive drum 1 tends to leak through the transfer material P. Therefore, when it is considered that the electric resistance of the transfer material P is low, even if a voltage having a value larger than the transfer voltage Vt is applied to the transfer roller 8 before the transfer material P reaches the fixing nip portion Nf, the transfer is performed. It is considered that an excessive current does not flow from the roller 8 to the photosensitive drum 1.

Based on the above, in this embodiment, transfer is performed from the transfer power source 18 at the timing when the tip of the second transfer material P2, which is considered to generate AC banding as in the first transfer material P1, reaches the transfer nip portion Nt. A transfer voltage Vt2 was applied to the roller 8. In this way, by applying the transfer voltage Vt2 from the transfer power supply 18 to the transfer roller 8 by the controller circuit 23 before the tip of the second transfer material P2 reaches the fixing nip portion Nf, the occurrence of AC banding is increased. It can be suppressed with probability.

(Example 4)
In the first embodiment, the control for changing the transfer voltage Vt when the controller circuit 23 determines that AC banding has occurred when executing one job has been described. On the other hand, in the fourth embodiment, when the plurality of jobs are executed, the first job is the second job following the first job in which the transfer voltage Vt is changed by determining that AC banding has occurred. It reflects the control of the controller circuit 23 in the job. In the present embodiment, the same configurations and controls as those in the first embodiment are designated by the same reference numerals as those in the first embodiment, and the description thereof will be omitted.

As described in Examples 2 and 3, the transfer materials P housed in the paper feed cassette 9 are placed in the same environment, and the types and states of the transfer materials P are substantially similar. I can think. Therefore, in the present embodiment, when it is determined that the types and states of the transfer materials P are substantially similar when executing a plurality of jobs, the first job is performed after the first job is completed. The voltage applied from the transfer power supply 18 to the transfer roller 8 is reflected in the second job.

For example, when the user does not access the paper cassette 9, it is considered that the types and states of the transfer materials P housed in the paper cassette 9 are substantially similar. Specifically, as one of the methods for detecting the presence / absence of access to the paper cassette 9 by the user, a detection unit for detecting the opening / closing of the paper cassette 9 may be provided. In this case, the controller circuit 23 is between the first job and the second job with respect to the first job and the second job that form an image on the transfer material P fed from the same paper cassette 9. , It is determined whether or not the paper feed cassette 9 has been opened and closed. Then, when it is determined that the AC banding has occurred in the first job because the paper cassette 9 has not been opened and closed, the transfer voltage Vt changed from the transfer voltage Vt by the controller circuit 23 in the first job A large value of voltage is reflected in the image formation of the second job.

When the signal of the second job is input to the controller circuit 23 during the image formation of the first job or the post-processing of the image formation of the first job, the user sends the paper feed cassette 9 to the paper cassette 9. It is also possible to determine that there is no access.

Further, for example, in the first job and the second job, the transfer material P is input to the controller circuit 23 from the detection means 19 in a state where the transfer material P is not sandwiched by the fixing nip portion Nf but sandwiched by the transfer nip portion Nt. The values of the currents may be stored and the following judgments may be made. That is, when the current detected by the detection means 19 in the first job and the current detected by the detection means 19 in the second job have substantially the same value, the first job and the second job are selected. It can be considered that the types and states of the transfer materials P used are almost similar. Therefore, in such a case, it is determined that the types and states of the transfer materials P are substantially similar, and the voltage applied from the transfer power supply 18 to the transfer roller 8 in the first job after the first job is completed. May be reflected in the second job.

In this embodiment, when it is determined that AC banding has occurred in the first job when a plurality of jobs are executed, the transfer power supply 18 is transferred to the transfer roller 8 in the first job in the second job. The applied voltage is reflected in the second job. With this configuration, it is not necessary to determine the occurrence of AC banding in the second job, and the occurrence of AC banding is suppressed from the first transfer material P to the last transfer material P in the second job. Is possible. Regarding the method of determining that the types and states of the transfer materials P are substantially similar in this embodiment, any one method may be used, or a plurality of methods may be combined for determination.

(Other Examples)
Although the above description has been made in accordance with the examples adapted to the monochrome image forming apparatus, the present invention is not limited to the above-mentioned examples. The present invention can be applied as long as it has a transfer member for transferring a toner image from an image carrier to a transfer material P and fixing means. That is, as shown in FIG. 15, the present invention can be applied to a color image forming apparatus, and the same effect can be obtained.

FIG. 15 is a schematic cross-sectional view illustrating the configuration of the image forming apparatus 300 of this embodiment. As shown in FIG. 1, the image forming apparatus 100 according to the present embodiment has image forming units SY and SM for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). , SC, and SK are arranged at regular intervals, and is a color image forming apparatus. In this embodiment, the configurations and operations of the image forming units SY, SM, SC, and SK are substantially the same except that the colors of the formed images are different. Therefore, the configuration of the image forming apparatus 300 of this embodiment will be described below using the image forming unit SK.

In the image forming apparatus 300 of this embodiment, the image signal transmitted from an information device such as a personal computer (not shown) is received and analyzed in the image forming apparatus 300, and then transmitted to the control means 323. Then, the control means 323 controls various means according to the information analyzed from the image signal, so that the image forming operation is started in the image forming apparatus 300.

The image forming apparatus SK includes a photosensitive drum 301K which is a drum-shaped photosensitive member, a charging roller 302K as a charging means, a developing roller 305K as a developing means, and a cleaning means 306K. When the image forming operation is started, the photosensitive drum 301K is rotationally driven in the direction of arrow R1 shown at a predetermined peripheral speed, and during the rotation process, the charging roller 302K has a predetermined polarity (negative electrode property in this embodiment) and a predetermined potential. Is uniformly charged. After that, an electrostatic latent image is formed on the surface of the photosensitive drum 301K by receiving exposure from the exposure means 304K according to the image signal. The electrostatic latent image formed on the surface of the photosensitive drum 301K is developed by the toner supplied from the developing roller 305K, and the toner image is formed on the photosensitive drum 301K.

On the opposite side of the photosensitive drum 301K, an endless intermediate transfer belt 307 as an image carrier stretched by tension rollers 327a to 327c as tension members is arranged, and the intermediate transfer belt 307 is indicated by arrow R32 in the drawing. It is driven to rotate in the direction. On the inner peripheral surface side of the intermediate transfer belt 307, a primary transfer roller 308K that presses the intermediate transfer belt 307 against the photosensitive drum 301K is arranged. Further, a primary transfer portion is formed at a position where the intermediate transfer belt 307 pressed by the primary transfer roller 308K and the photosensitive drum 301K come into contact with each other. The toner image formed on the photosensitive drum 301K is first transferred from the photosensitive drum 301K to the intermediate transfer belt 307 in the process of passing through the primary transfer unit. In this way, the toner images of each color are primarily transferred to the intermediate transfer belt 307 in each image forming unit SY, SM, SC, and SK, and the intermediate transfer belt 307 has a plurality of color toner images corresponding to the target color image. It is formed.

A secondary transfer roller 328 as a transfer member is arranged on the opposite side of the tension roller 327a via an intermediate transfer belt 307 as an image carrier, and a position where the intermediate transfer belt 307 and the secondary transfer roller 328 come into contact with each other. A secondary transfer portion Nt3 is formed in the transfer portion. The secondary transfer roller 328 is connected to the transfer power supply 318, and the control means 323 controls the transfer power supply 318 and applies a voltage to the secondary transfer roller 328 to apply a plurality of colors from the intermediate transfer belt 307 to the transfer material P. The toner image of is secondarily transferred. Further, a detection means 319 capable of detecting the current flowing through the secondary transfer roller 328 is provided between the transfer power supply 318 and the secondary transfer roller 328.

The transfer material P loaded on the paper cassette 9 is supplied from the paper cassette 9 by the paper feed roller 311 at the timing when the toner images of the plurality of colors formed on the intermediate transfer belt 307 reach the secondary transfer unit. It is fed and transported to the secondary transfer unit Nt3. The transfer material P to which the toner images of a plurality of colors are secondarily transferred in the secondary transfer unit Nt3 is conveyed to the fixing means 314, heated and pressurized by the heating means 331 and the pressurizing means 330, and the toners of each color are melt-mixed. Is fixed to the transfer material P. After that, the transfer material P is discharged to the paper discharge tray 317 as a loading portion by the paper discharge roller 316.

1 Photosensitive drum (image carrier)
8 Transfer roller (transfer member)
14 Fixing means 18 Transfer power supply 19 Detection means 23 Controller circuit (control means)
24 Environment sensor (second detection means)
30 Pressurizing member 31 Heating member 31b Heater (heating part)
52 Commercial power supply (AC power supply)

Claims (21)

An image carrier that supports a toner image, a transfer member that forms a transfer portion in contact with the image carrier, and transfers a toner image from the image carrier to a transfer material at the transfer portion, and a transfer member. A transfer power source to which a voltage is applied, a first detection means arranged between the transfer member and the transfer power source for detecting a current flowing through the transfer member, and a control means for controlling the transfer power source. In an image forming apparatus including a fixing means arranged downstream of the transfer portion in a transport direction of the transfer material and having a heating member and a pressurizing member that abuts on the heating member to form a fixing portion. ,
A second detecting means for detecting the temperature or humidity of the ambient environment of the image forming apparatus is provided.
The heating member has a heating portion arranged so as to face the transfer material sandwiched between the fixing portions.
The heating unit heats the transfer material sandwiched between the fixing parts by applying a voltage from the AC power source.
The control means includes a frequency obtained from a first detection result input from the first detection means when transferring a toner image from the image carrier to the transfer material in the transfer unit, and a power source of the AC power supply. It is possible to control the transfer power supply according to the result of comparison with a predetermined frequency range including a frequency.
When the frequency obtained from the first detection result is included in the predetermined frequency range, the control means controls the transfer power supply according to the second detection result input from the second detection means. An image forming apparatus, characterized in that a voltage applied to the transfer member is set. The control means applies a voltage applied to the transfer member from the transfer power source when the transfer power source is controlled so that a current of a predetermined value flows through the transfer member in a state where the transfer material is not sandwiched between the transfer portions. The first transfer voltage applied from the transfer power source to the transfer member when the toner image is transferred from the image carrier to the transfer material in the transfer unit is determined according to the value of. The image forming apparatus according to 1. The control means includes a frequency obtained from the first detection result in the predetermined frequency range, and the temperature or humidity detected by the second detection means is equal to or higher than a predetermined value. The image forming apparatus according to claim 2, wherein in some cases, the voltage applied from the transfer power source to the transfer member is changed from the first transfer voltage. When the temperature or humidity detected by the second detecting means is less than the predetermined value, the control means applies a voltage applied from the transfer power source to the transfer member from the first transfer voltage. The image forming apparatus according to claim 3, wherein the image forming apparatus is not changed. The control means includes a third detection means for detecting the voltage output from the AC power supply, and the control means includes the frequency obtained from the first detection result in the predetermined frequency range and the first. 2. The second or second aspect, wherein the voltage applied to the transfer member from the transfer power supply is changed from the first transfer voltage when the voltage detected by the detection means 3 is equal to or higher than a predetermined value. The image forming apparatus according to 3. The control means determines the type of transfer material conveyed to the transfer unit from the print mode input to the control means, and the frequency obtained from the first detection result is included in the predetermined frequency range. The second or third aspect of the present invention, wherein the voltage applied to the transfer member from the transfer power source is changed from the first transfer voltage according to the type of the transfer material obtained from the print mode. Image forming device. A fourth detection means for detecting the type of transfer material conveyed to the transfer unit is provided, and the control means is used when the frequency obtained from the first detection result is included in the predetermined frequency range. The second or third claim is characterized in that the voltage applied from the transfer power source to the transfer member is changed from the first transfer voltage according to the type of the transfer material detected by the fourth detection means. The image forming apparatus according to the description. An image carrier that supports a toner image, a transfer member that forms a transfer portion in contact with the image carrier, and transfers a toner image from the image carrier to a transfer material at the transfer portion, and a transfer member. A transfer power source to which a voltage is applied, a first detection means arranged between the transfer member and the transfer power source for detecting a current flowing through the transfer member, and a control means for controlling the transfer power source. In an image forming apparatus including a fixing means arranged downstream of the transfer portion in a transport direction of the transfer material and having a heating member and a pressurizing member that abuts on the heating member to form a fixing portion. ,
The heating member has a heating portion arranged so as to face the transfer material sandwiched between the fixing portions, and the heating portion is sandwiched between the fixing portions by applying a voltage from an AC power source. Heat and
The control means includes a frequency obtained from a first detection result input from the first detection means when transferring a toner image from the image carrier to the transfer material in the transfer unit, and a power source of the AC power supply. It is possible to control the transfer power supply according to the result of comparison with a predetermined frequency range including a frequency, and determine the type of transfer material to be conveyed to the transfer unit from the information input to the control means. Is possible,
When the frequency obtained from the first detection result is included in the predetermined frequency range, the control means receives the transfer member from the transfer power source according to the type of transfer material conveyed to the transfer unit. An image forming apparatus characterized in that a voltage applied to is set. The control means applies a voltage applied to the transfer member from the transfer power source when the transfer power source is controlled so that a current of a predetermined value flows through the transfer member in a state where the transfer material is not sandwiched between the transfer portions. The first transfer voltage applied from the transfer power source to the transfer member when the toner image is transferred from the image carrier to the transfer material in the transfer unit is determined according to the value of. 8. The image forming apparatus according to 8. When the frequency obtained from the first detection result is included in the predetermined frequency range, the control means receives the transfer member from the transfer power source according to the type of transfer material conveyed to the transfer unit. The image forming apparatus according to claim 9, wherein the voltage applied to is changed from the first transfer voltage. The image forming apparatus according to any one of claims 8 to 10, wherein the control means determines the type of transfer material to be conveyed to the transfer unit from a print mode input to the control means. .. A fourth detection means for detecting the type of transfer material conveyed to the transfer unit is provided, and the control means is used when the frequency obtained from the first detection result is included in the predetermined frequency range. The ninth or tenth aspect of the present invention is characterized in that the voltage applied from the transfer power source to the transfer member is changed from the first transfer voltage according to the type of the transfer material detected by the fourth detection means. The image forming apparatus according to the description. The heating member has a tubular flexible member that covers the heating portion, and the heating portion is arranged at a position facing the pressurizing member via the flexible member. The image forming apparatus according to any one of claims 1 to 12. The heating unit includes a substrate, an electrode unit to which a voltage from the AC power source is applied, and a heat generating resistor formed on the surface of the substrate, and the heat generating resistor is from the AC power source. When a voltage is applied to the electrode portion, an electric current flows through the electrode portion to generate heat, and when the heat generation resistor generates heat, the heating portion heats the transfer material sandwiched between the fixing portions. The image forming apparatus according to any one of claims 1 to 13, wherein the image forming apparatus can be used. A bidirectional thyristor is arranged between the electrode portion and the AC power supply, and the control means controls the current flowing through the bidirectional thyristor to apply a voltage applied to the electrode portion from the AC power supply. The image forming apparatus according to claim 14, wherein the image forming apparatus is controlled. Regarding the first detection result, a point in which the slope of the second waveform obtained by taking the simple moving average of the first waveform changes after the first waveform is obtained by taking the simple moving average once. The image forming apparatus according to any one of claims 1 to 15, wherein the frequency is determined to be a peak, and the frequency obtained from the time between adjacent peaks is compared with the predetermined frequency range. The adjacent peaks are a first peak in which the slope of the second waveform changes from positive to negative and a second peak in which the slope of the second waveform changes from negative to positive. The image forming apparatus according to claim 16, wherein a frequency obtained from the time between the second peaks is compared with the predetermined frequency range. In the second waveform, when the difference in current value between the first peak and the second peak is equal to or greater than a predetermined value, the time between the first peak and the second peak is reached. The image forming apparatus according to claim 17, wherein the frequency obtained from the time is compared with the predetermined frequency range. In the second waveform, when the difference in current values between adjacent peaks is equal to or greater than a predetermined value for at least three consecutive peaks, the frequency obtained from the time between the adjacent peaks is used. The image forming apparatus according to any one of claims 16 to 18, wherein the image forming apparatus is compared with the predetermined frequency range. Any of claims 1 to 19, wherein the image carrier is provided with a developing means for supplying a toner image to the image carrier, and the image carrier is a photoconductor on which an electrostatic latent image is developed by the developing means. The image forming apparatus according to item 1. The image according to any one of claims 1 to 20, wherein the image carrier is an endless intermediate transfer belt that carries a toner image transferred from the photoconductor. Forming device.

Images